E-commerce power Amazon.com blasted federal regulators on Tuesday for being slow to approve commercial drone testing, saying the United States is falling behind other countries in the potentially lucrative area of unmanned aviation technology.

Less than a week after the Federal Aviation Administration gave Amazon.com the green light to test a delivery drone outdoors, the company told U.S. lawmakers that the prototype drone had already become obsolete while the company waited more than six months for the agency's permission.

"We don't test it anymore. We've moved on to more advanced designs that we already are testing abroad," said Paul Misener, Amazon.com's vice president for global public policy.

"Nowhere outside of the United States have we been required to wait more than one or two months to begin testing," Misener said in written testimony submitted to the Senate Subcommittee on Aviation Operations, Safety and Security.

Misener said Amazon had applied on Friday for permission to test a more advanced drone system and now hopes for quicker approval.

The Amazon.com case illustrates the frustrations of many companies and industry lobbyists, who say the U.S. regulatory process is not keeping up with rapidly developing drone technology that could generate new revenues and cost savings for a range of industries.

Misener, who was scheduled to join a witness panel at the subcommittee hearing, said European and other international authorities have more "reasonable" approaches that recognize the potential economic benefits of commercial drone operations.

"This low level of government attention and slow pace are inadequate, especially compared to the regulatory efforts in other countries," Misener said.

"The (FAA) already has adequate statutory authority. What the FAA needs is impetus, lest the United States fall further behind," he added.

Seattle-based Amazon.com, the largest e-commerce company in the United States, wants to use drones to deliver packages to its customers over distances of 10 miles (16 km)or more, which would require drones to travel autonomously while equipped with technology to avoid collisions with other aircraft.

The FAA recently proposed rules that would lift the current ban on most commercial drone flights, but several restrictions attached would make package delivery and other business applications unfeasible.

Among other constraints, the proposed rules would limit commercial drones to an altitude of 500 feet (150 meters), allow flights only during daytime and require operators to keep the aircraft in sight at all times.

The agency does not expect to finalize the rules until late 2016 or early 2017, according to government officials. During this period, the current ban will stay in place; companies can apply for exemptions to use drones for specific business applications.

The FAA has been slow to grant exemptions, however, granting only 48 of several hundred requests.

The Republican-led subcommittee called the hearing to examine the agency's efforts to integrate unmanned aircraft systems, or UAS, safely into U.S. airspace. Industry forecasters say that drones would generate nearly $14 billion of U.S. economic activity in the first three years of integration and $82 billion over a decade.

Meanwhile, Australia, Canada, France and the United Kingdom have progressed toward airspace integration and allow for commercial use, the Government Accountability Office (GAO) said in a report to the subcommittee.

Australia has granted operating certificates to 185 businesses, while several European countries have granted licenses to more than 1,000 operators, according to the report.

While the GAO said overseas restrictions are similar to those proposed by the FAA, it noted that France has begun to allow beyond-line-of-sight operations on a limited basis.